I think you can have two flavors of product marketers. The first are very analytical and business-minded. They identify the key top customer problems and benefits for the product. Then, they might need to collaborate with someone in brand, content, or copywriting to make those messaging points spiffier and more engaging. I am in this camp!
Other PMMs are great wordsmiths who take pride in choosing just the right word to get to the essence of the point they are trying to make. Both can be good product marketers.
I believe product marketers, at minimum, need to be good at writing long-form content. It’s not only fine but common to ask for help tightening up messaging for short-form like headlines, which is an art in itself.